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all right everyone thanks for coming in.

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This is the missing semester of your CS Education;

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at least that's what we chose to call

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the class. if you're not here for this

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class then you're in the wrong room. We

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will be here for about an hour just to

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set your expectations and I want to talk

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to you a little bit first about why

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we're doing this class. So this class

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stems out of an observation that Anish

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and Jose and I have made while TA-ing various

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classes at MIT which is that basically

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all of us computer scientists, we know

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that computers are great at doing these

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repetitive tasks and automating things

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but we often fail to realize that there

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are lots of tools that can make our own

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development processes better. We can be a

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lot more efficient about how we use our

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computers because we can use the

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computer as a tool for ourselves not

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just for building websites or software

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those sorts of things and this class is

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an attempt to address - this is an attempt

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to show you some of the tools that you

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can use to great effect in your day to

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day in your research and in your studies

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and it's going to be a class where we

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want you to teach you both how to make

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the most of the tools that you already

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know but also hopefully teach you about

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some tools so you don't know from before

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and how to combine those tools to

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produce more powerful things than you

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think you might be able to do with what

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you know today the class is going to be

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structured as a series of 11 one-hour

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lectures and each one is going to cover

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a particular topic you can see the

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website which is also listed there for

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the list of lecture topics and what date

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will do each one they will mostly be

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independent and so you can sort of show

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up for the ones that you're interested

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in but we will sort of assume that

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you've been following along so that as

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we get to later lectures I'm not going

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to be teaching you bash all over again

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for example we we are also going to post

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both the lecture notes and recordings of

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the lectures online exactly when we do

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that we haven't established yet but it

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will be after the lectures obviously the

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videos have to be posted after

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the class is gonna be run by me John and

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Anne each sitting over there and Jose

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who is not currently here but we'll be

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holding tomorrow's lecture and keep in

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mind that we're trying to cover a lot of

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ground over the course of just 11

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one-hour lectures and so we will be

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moving relatively rapidly but please do

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stop us if there's anything where you

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feel like you're not following along if

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you feel like there's something you wish

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we would spend more time on just let us

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know please interrupt us with questions

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and also after each lecture we're going

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to hold office hours on the ninth floor

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of building 30 to the Stata Center of

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the computer science building as if you

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show up up in the ninth floor lounge

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there and the gates tower then you can

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come and try some of the exercises that

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we give for each lecture or just ask us

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other questions about things we've

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talked about in lecturer or other things

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about using your computer efficiently

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due to the limited time that we have

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available we're not going to be able to

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cover all tools and full detail and so

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we'll try to do is highlight interesting

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tools and interesting ways to use them

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we won't necessarily dig into the deep

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details about how all of it works or

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more elaborate use cases but if you have

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questions about them please come ask us

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about that too many of these tools are

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tools that we have used for years and we

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might be able to point you to additional

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interesting things you can do with them

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sort of like take advantage of the fact

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that we're here this class is going to I

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don't wanna say ramped up quickly but

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what's going to happen over the course

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of this particular lecture is that we'll

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cover many of the basics that we assume

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that you will know for the rest of the

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semester things like how to use your

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shell and your terminal and I'll explain

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what those are - those who you're not

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familiar with them and then will pretty

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quickly ramp up into more advanced tools

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and how to use them you can already see

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from the lecture notes the kind of

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topics that we're going to be covering

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and so that brings us to today's lecture

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in which we are going to cover the shell

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and the shell is going to be one of the

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primary ways that you interact with your

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computer once you want to do more things

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than what the sort of visual interfaces

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you might be used to allow you to do the

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visual interfaces are sort of limited in

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what

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they allow you to do because you can

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only do the things that there are

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buttons for sliders for input fields for

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often these textual tools are built to

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be both composable with one another but

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also to have tons of different ways to

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combine them or ways to program and

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automate them and that is why in this

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class we will be focusing on these

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command line or text-based tools and the

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shell is the place that you would do

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most of this work so for those of you

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are not familiar with the shell most

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platform provides some kind of shell on

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Windows this is often PowerShell but

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there are also other shells available on

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Windows on Linux you will find tons of

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terminals these are windows that allow

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you to display shells and you'll also

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find many different types of shells the

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most common of which is bash or the born

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again shell because it's such a common

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shell it is the one we're primarily

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going to be covering in these lectures

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if you're on Mac OS you will probably

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also have bash maybe an older version of

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it if you open the terminal app and so

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if you want to follow along on any of

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these platforms feel free but keep in

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mind that most of this is going to be

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sort of Linux centric in terms of how we

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teach it even though most of these tools

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work on all the platforms if you want to

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install a terminal and a shell and you

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don't know how to do it well we're happy

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to show you at office hours or it's

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usually very easy to just Google like

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your platform plus like terminal and you

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will get one now when you open a

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terminal you get something that looks a

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little bit like this so it will usually

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have just a single line at the top and

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this is what's known as the shell prompt

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you can see that my shell prompt looks

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like this it has my user name the name

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of the machine that I'm on the current

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path I'm on and we will talk about paths

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a little bit later and then it's really

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just sort of blinking they're asking me

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for input and this is the shell prompt

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where you tell the shell what you want

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it to do and you can customize this

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prompt a lot and when you open it on

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your machine it might not look exactly

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like this it might look something like

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this if you've configured it a little or

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it might look all sorts of different

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ways we won't go too much into

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customizing your shell in this

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particularly

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we'll do that later here we're just

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going to talk about how do you use this

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shell to do useful things and this is

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our the main textual interface you have

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to your computer's through this shell on

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the shell prompt you get to write

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commands and commands can be relatively

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straightforward things usually it'll be

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something like executing programs with

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arguments what does that look like well

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one program we can execute is the date

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program we just type date and press

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enter and then it will show you

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unsurprisingly the date and time you can

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also execute a program with arguments

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this is one way to modify the behavior

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of the program so for example there is a

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program called echo and echo just prints

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out the arguments that you give it and

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arguments are just white space separated

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things that follow the program name so

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we can say hello and then it will print

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hello back

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perhaps not terribly surprising but this

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is the very basics of arguments one

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thing that you'll notice is that I said

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that arguments are separated by

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whitespace and you might wonder well

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what if I want an argument as multiple

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words you can also quote things so you

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can do things like echo hello space

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world and now the echo program receives

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one argument that contains the string

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hello world with a space well you can

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also use single quotes for this and the

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difference between single quotes and

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double quotes will get back to and when

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we talk about bash scripting you can

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also just escape single characters so

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for example hello world this will also

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work just fine all of these rules about

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how you escape and how you parse and

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quote various arguments and variables

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we'll cover a little bit later hopefully

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you won't run into too many we oughta

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tease about this just keep in mind at

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least that spaces separate arguments so

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if you want to do something like make a

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directory called my photos

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you can't just type like make directory

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my photos it will create two directories

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one called my and one called photos and

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that is probably not what you want now

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one thing you might ask is how does the

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shell know what these programs are when

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I type date or when I type echo how does

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it know what these programs are supposed

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to do and the answer to this is your

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program your

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computer has a bunch of built-in

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programs that comes with the machine

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just like you your machine my chip with

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like the terminal app or it might chip

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with like Windows Explorer or at my chip

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with some kind of browser it also ships

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with a bunch of terminal centric

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applications and these are stored on

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your file system and your shell has a

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way to determine where a program is

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located basically has a way to search

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for programs it does this through

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something called an invariant

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environment variable an environment

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variable is a variable like you might be

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used to for programming languages it

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turns out that the shell and the

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bourne-again shell in particular is

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really a programming language this

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prompt that you're given here is not

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just able to run a program with

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arguments. You can also do things like

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while loops, for loops, conditionals...

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All of these - you can define

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functions, you can have variables, and all

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of these things you can do in the shell.

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We'll cover a lot of that in the next

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lecture, on shell scripting. For now,

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though, let's just look at this

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particular environment variable.

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Environment variables are things that

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are set whenever you start your shell

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they're not things you have to set every

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time you run your shell there are a

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bunch of these that are set things like

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where is your home directory what is

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your username and there's also one

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that's critical for this particular

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purpose which is the path variable so if

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I echo out dollar path this is going to

275
00:10:18,930 --> 00:10:25,100
show me all of the paths on my machine

276
00:10:22,589 --> 00:10:27,930
that the shell will search for programs

277
00:10:25,100 --> 00:10:30,870
you'll notice that this is a list that

278
00:10:27,930 --> 00:10:33,000
is colon separated it might be kind of

279
00:10:30,870 --> 00:10:36,000
long and hard to read but the essentials

280
00:10:33,000 --> 00:10:38,279
is that - whenever you type the name of

281
00:10:36,000 --> 00:10:41,610
a program is gonna search through this

282
00:10:38,279 --> 00:10:43,769
list of paths on your machine and it's

283
00:10:41,610 --> 00:10:46,920
gonna look in each directory for a

284
00:10:43,769 --> 00:10:49,110
program or a file whose name matches the

285
00:10:46,920 --> 00:10:51,029
command you try to run so in my case

286
00:10:49,110 --> 00:10:52,800
when I try to run date or echo it's

287
00:10:51,029 --> 00:10:54,509
gonna walk through these one at a time

288
00:10:52,800 --> 00:10:56,370
until it finds one that contains the

289
00:10:54,509 --> 00:10:58,410
program called date or echo and then

290
00:10:56,370 --> 00:11:00,000
it's gonna run it if we want to know

291
00:10:58,410 --> 00:11:01,649
which one it actually runs there's a

292
00:11:00,000 --> 00:11:04,620
command called which which lets us do

293
00:11:01,649 --> 00:11:07,500
that so I can type which echo and will

294
00:11:04,620 --> 00:11:10,830
tell me that if I were to run a program

295
00:11:07,500 --> 00:11:12,720
called echo I would run this one it's

296
00:11:10,830 --> 00:11:16,350
worth pausing here to talk about what

297
00:11:12,720 --> 00:11:18,620
paths are so paths are a way to name the

298
00:11:16,350 --> 00:11:21,630
location of a file on your computer on

299
00:11:18,620 --> 00:11:24,780
Linux and Oh Mac OS these paths are

300
00:11:21,630 --> 00:11:28,170
separated by slashes forward slashes so

301
00:11:24,780 --> 00:11:30,930
you'll see here that this is in the in

302
00:11:28,170 --> 00:11:32,760
the root directory so the slash at the

303
00:11:30,930 --> 00:11:34,850
very beginning indicates that this is

304
00:11:32,760 --> 00:11:37,710
starting from the top of the file system

305
00:11:34,850 --> 00:11:40,980
then look inside the directory called

306
00:11:37,710 --> 00:11:43,580
USR then look inside the directory bin

307
00:11:40,980 --> 00:11:46,440
and then look for the file called echo

308
00:11:43,580 --> 00:11:48,620
on windows paths like this are usually

309
00:11:46,440 --> 00:11:51,900
separated by back slashes instead and

310
00:11:48,620 --> 00:11:53,640
we're on Linux and Mac OS everything

311
00:11:51,900 --> 00:11:56,370
lives under the root name space so all

312
00:11:53,640 --> 00:12:00,270
paths start with a slash or all absolute

313
00:11:56,370 --> 00:12:02,070
paths on Windows there is one root for

314
00:12:00,270 --> 00:12:05,130
every partition so you might have seen

315
00:12:02,070 --> 00:12:08,220
things like C colon backslash or D colon

316
00:12:05,130 --> 00:12:11,340
backslash so Windows has separate sort

317
00:12:08,220 --> 00:12:13,050
of file system path hierarchies for each

318
00:12:11,340 --> 00:12:14,850
each Drive that you have

319
00:12:13,050 --> 00:12:18,540
whereas on Linux and Mac OS these are

320
00:12:14,850 --> 00:12:20,010
all mounted under one namespace you'll

321
00:12:18,540 --> 00:12:21,690
notice that I said the word absolute

322
00:12:20,010 --> 00:12:27,360
path and you might not know what that

323
00:12:21,690 --> 00:12:29,460
means so absolute paths are paths that

324
00:12:27,360 --> 00:12:31,890
fully determine the location of a file

325
00:12:29,460 --> 00:12:33,720
so in this case this is saying this is

326
00:12:31,890 --> 00:12:36,540
talking only about a specific echo file

327
00:12:33,720 --> 00:12:39,030
and it's giving you the the full path to

328
00:12:36,540 --> 00:12:42,839
that file but there are also things

329
00:12:39,030 --> 00:12:45,240
known as relative paths so a relative

330
00:12:42,839 --> 00:12:49,320
path is relative to where you currently

331
00:12:45,240 --> 00:12:52,490
are and so the way we find out where we

332
00:12:49,320 --> 00:12:56,190
currently are is you can type PWD for

333
00:12:52,490 --> 00:13:00,060
present working directory present print

334
00:12:56,190 --> 00:13:02,700
working directory so if I type PWD it

335
00:13:00,060 --> 00:13:05,790
will print out the current path that I'm

336
00:13:02,700 --> 00:13:08,220
in right so currently I'm in the home

337
00:13:05,790 --> 00:13:11,030
directory under the root and then John

338
00:13:08,220 --> 00:13:14,730
under that and then dev under that etc

339
00:13:11,030 --> 00:13:16,770
from here I can then choose to change my

340
00:13:14,730 --> 00:13:18,540
current working directory and all

341
00:13:16,770 --> 00:13:20,190
relative paths are relative to the

342
00:13:18,540 --> 00:13:21,329
current working directory which is

343
00:13:20,190 --> 00:13:24,629
basically where you

344
00:13:21,329 --> 00:13:28,709
they are in this case for example I can

345
00:13:24,629 --> 00:13:30,449
do CD / home CDs change directory this

346
00:13:28,709 --> 00:13:32,610
is the way that I change what my current

347
00:13:30,449 --> 00:13:34,829
working directory is in this case I

348
00:13:32,610 --> 00:13:37,889
change to home and I am now you'll see

349
00:13:34,829 --> 00:13:40,619
my my shell prompt change to say that I

350
00:13:37,889 --> 00:13:42,660
am now in home it just gives me the name

351
00:13:40,619 --> 00:13:44,220
of the last segment of the path but you

352
00:13:42,660 --> 00:13:45,509
can also configure your terminal to give

353
00:13:44,220 --> 00:13:50,309
you the full path whenever you're

354
00:13:45,509 --> 00:13:53,100
anywhere and now if I type PWD again it

355
00:13:50,309 --> 00:13:54,869
will tell me I'm in slash home there are

356
00:13:53,100 --> 00:13:59,100
also a couple of special directories

357
00:13:54,869 --> 00:14:03,149
that exist there is dot and dot dot dot

358
00:13:59,100 --> 00:14:05,129
means the current directory dot dot

359
00:14:03,149 --> 00:14:06,749
means the parent directory so this is a

360
00:14:05,129 --> 00:14:09,540
way that you can easily navigate around

361
00:14:06,749 --> 00:14:13,079
the system for example here if I type CD

362
00:14:09,540 --> 00:14:15,179
dot dot it will tell me that I am now in

363
00:14:13,079 --> 00:14:17,639
slash so I'm now in the root of the file

364
00:14:15,179 --> 00:14:22,139
system I was in slash home now I'm in

365
00:14:17,639 --> 00:14:24,869
slash and indeed if I type PWD well it

366
00:14:22,139 --> 00:14:26,790
will do that right thing and I can also

367
00:14:24,869 --> 00:14:28,980
then use relative paths to go down into

368
00:14:26,790 --> 00:14:31,769
the file system right so I can do CD dot

369
00:14:28,980 --> 00:14:34,079
slash home and this is gonna CD into the

370
00:14:31,769 --> 00:14:36,899
home directory under the current

371
00:14:34,079 --> 00:14:39,839
directory right so this will bring me

372
00:14:36,899 --> 00:14:42,119
back to slash home if I now tried CD dot

373
00:14:39,839 --> 00:14:44,100
slash home again it will say there's no

374
00:14:42,119 --> 00:14:45,569
such directory because there is no home

375
00:14:44,100 --> 00:14:49,429
directory under the current directory

376
00:14:45,569 --> 00:14:53,699
I'm on which I changed by doing CD right

377
00:14:49,429 --> 00:14:57,509
and I can sort of see de all the way

378
00:14:53,699 --> 00:15:01,110
back to the place that I was using

379
00:14:57,509 --> 00:15:07,040
relative paths and I can also do things

380
00:15:01,110 --> 00:15:09,059
like dot dot dot dot dot to get back to

381
00:15:07,040 --> 00:15:10,649
somewhere deep in my file system this

382
00:15:09,059 --> 00:15:13,019
happens to be all the way back to the

383
00:15:10,649 --> 00:15:15,629
root so here there's a bin directory and

384
00:15:13,019 --> 00:15:17,850
another bin there's an echo file and so

385
00:15:15,629 --> 00:15:20,309
then I could do world and that runs the

386
00:15:17,850 --> 00:15:22,079
echo program under bin alright so this

387
00:15:20,309 --> 00:15:24,439
is a way that you can construct paths to

388
00:15:22,079 --> 00:15:26,579
arbitrarily traverse your filesystem

389
00:15:24,439 --> 00:15:28,379
sometimes you want to absolute paths and

390
00:15:26,579 --> 00:15:29,789
sometimes you want relative ones usually

391
00:15:28,379 --> 00:15:33,179
you want to use whichever one is shorter

392
00:15:29,789 --> 00:15:34,390
but if you want to for example run a

393
00:15:30,629 --> 00:15:34,390
program or write

394
00:15:34,390 --> 00:15:38,980
a program that runs the program like

395
00:15:36,940 --> 00:15:41,830
echo or date and you want it to be able

396
00:15:38,980 --> 00:15:43,660
to run be run from anywhere you either

397
00:15:41,830 --> 00:15:45,640
want to just give the name of the

398
00:15:43,660 --> 00:15:47,770
program like date or echo and let the the

399
00:15:45,640 --> 00:15:49,720
shell use the path to figure out where

400
00:15:47,770 --> 00:15:51,670
it is or you want to give its absolute

401
00:15:49,720 --> 00:15:53,500
path because if you gave a relative path

402
00:15:51,670 --> 00:15:55,840
then if I ran it in my home directory

403
00:15:53,500 --> 00:16:01,720
and you ran it in some other directory

404
00:15:55,840 --> 00:16:04,600
it might work for me but not for you in

405
00:16:01,720 --> 00:16:06,340
general when we run a program it is

406
00:16:04,600 --> 00:16:08,320
going to be operating on the current

407
00:16:06,340 --> 00:16:09,910
working directory at least by default

408
00:16:08,320 --> 00:16:11,980
unless we give it any other arguments

409
00:16:09,910 --> 00:16:13,750
and this is really handy because it

410
00:16:11,980 --> 00:16:15,730
means that often we don't have to give

411
00:16:13,750 --> 00:16:17,680
full paths for things we can just use

412
00:16:15,730 --> 00:16:20,050
the name of files and in the directory

413
00:16:17,680 --> 00:16:22,570
that we're currently in one thing that's

414
00:16:20,050 --> 00:16:24,280
really useful is to figure out what is

415
00:16:22,570 --> 00:16:26,410
in the current directory we're in so we

416
00:16:24,280 --> 00:16:28,060
already saw PWD which prints where you

417
00:16:26,410 --> 00:16:31,090
currently are there's a command called

418
00:16:28,060 --> 00:16:33,310
LS which will show you it will list the

419
00:16:31,090 --> 00:16:35,980
files in the current directory so if i

420
00:16:33,310 --> 00:16:38,050
type LS here this is all the files in

421
00:16:35,980 --> 00:16:39,850
the current directory right and this is

422
00:16:38,050 --> 00:16:43,420
a handy way to just quickly navigate

423
00:16:39,850 --> 00:16:46,930
through the filesystem you'll see that

424
00:16:43,420 --> 00:16:48,490
if I sort of CD dot and then do LS it'll

425
00:16:46,930 --> 00:16:53,370
show me the files in that directory

426
00:16:48,490 --> 00:16:56,260
instead but with LS I can also give it

427
00:16:53,370 --> 00:16:58,360
LS dot dot like I can give it a path and

428
00:16:56,260 --> 00:16:59,920
then will LS that file instead of the

429
00:16:58,360 --> 00:17:04,270
one that I'm currently in or LS that

430
00:16:59,920 --> 00:17:05,829
directory and you can see this if I go

431
00:17:04,270 --> 00:17:09,220
all the way to the root as well right

432
00:17:05,829 --> 00:17:11,560
root has different files one handy trick

433
00:17:09,220 --> 00:17:13,570
you might not know about here is there

434
00:17:11,560 --> 00:17:16,570
are two other special things you can do

435
00:17:13,570 --> 00:17:18,339
one is the tilde character this

436
00:17:16,570 --> 00:17:21,130
character brings you to your home

437
00:17:18,339 --> 00:17:23,140
directory so tilde always expands to the

438
00:17:21,130 --> 00:17:25,780
home directory and you can do relative

439
00:17:23,140 --> 00:17:30,040
paths to it so I can do tilde slash dev

440
00:17:25,780 --> 00:17:32,980
slash P DOS classes missing semester and

441
00:17:30,040 --> 00:17:36,670
now I'm there because tilde expanded to

442
00:17:32,980 --> 00:17:39,460
slash home slash John there is also for

443
00:17:36,670 --> 00:17:42,250
CD in particular a really handy argument

444
00:17:39,460 --> 00:17:44,530
you can give which is - if you do CD -

445
00:17:42,250 --> 00:17:47,380
it will CD to the directory you were

446
00:17:44,530 --> 00:17:48,180
previously in so if I do CD - I go back

447
00:17:47,380 --> 00:17:52,230
to root

448
00:17:48,180 --> 00:17:53,880
if I do CD - again I go back to missing

449
00:17:52,230 --> 00:17:55,080
semester so this is a handy way if you

450
00:17:53,880 --> 00:18:01,290
want to toggle between two different

451
00:17:55,080 --> 00:18:03,570
directories in the case of LS or in the

452
00:18:01,290 --> 00:18:06,180
case of CD there might be arguments do

453
00:18:03,570 --> 00:18:07,560
you don't know about right currently we

454
00:18:06,180 --> 00:18:09,510
haven't really been doing anything

455
00:18:07,560 --> 00:18:11,520
except giving paths but how do you even

456
00:18:09,510 --> 00:18:14,250
discover that you can give a path to LS

457
00:18:11,520 --> 00:18:16,530
in the first place well most programs

458
00:18:14,250 --> 00:18:18,840
take what are known as arguments like

459
00:18:16,530 --> 00:18:21,570
flags and options these are things that

460
00:18:18,840 --> 00:18:24,810
usually start with a - one of the Hemi

461
00:18:21,570 --> 00:18:26,880
is one of these is - help most programs

462
00:18:24,810 --> 00:18:30,000
implement this and if you run for

463
00:18:26,880 --> 00:18:34,020
example LS - help it all helpfully print

464
00:18:30,000 --> 00:18:36,000
out a bunch of information about that

465
00:18:34,020 --> 00:18:38,400
command and you'll see here that it says

466
00:18:36,000 --> 00:18:40,260
the usage is LS and you can give some

467
00:18:38,400 --> 00:18:42,030
number of options and you can give some

468
00:18:40,260 --> 00:18:46,350
number of files the way to read that

469
00:18:42,030 --> 00:18:48,600
usage line is triple dot means one like

470
00:18:46,350 --> 00:18:50,850
zero or one or more and the square

471
00:18:48,600 --> 00:18:52,890
bracket means optional so in this case

472
00:18:50,850 --> 00:18:54,300
there's an optional number of options

473
00:18:52,890 --> 00:18:56,790
and there's an optional number of files

474
00:18:54,300 --> 00:18:58,740
and you'll see that it says what the

475
00:18:56,790 --> 00:19:00,720
program does and also specifies a number

476
00:18:58,740 --> 00:19:03,000
of different types of flags and options

477
00:19:00,720 --> 00:19:04,950
you can give usually we call things that

478
00:19:03,000 --> 00:19:07,830
are a single dash in a single letter a

479
00:19:04,950 --> 00:19:09,900
flag and anything that or anything that

480
00:19:07,830 --> 00:19:11,730
doesn't take a value a flag and anything

481
00:19:09,900 --> 00:19:16,640
that does take a value an option so for

482
00:19:11,730 --> 00:19:22,260
example - a and - all are both flags and

483
00:19:16,640 --> 00:19:24,180
- C or - color R is an option one thing

484
00:19:22,260 --> 00:19:30,330
you'll see under here if you scroll down

485
00:19:24,180 --> 00:19:37,140
far enough is the - L flag and that's

486
00:19:30,330 --> 00:19:39,480
unhelpful the - L flag the - L flag uses

487
00:19:37,140 --> 00:19:40,860
a long listing format now that's

488
00:19:39,480 --> 00:19:43,350
particularly helpful in and of itself

489
00:19:40,860 --> 00:19:46,890
but let's see what it actually does so

490
00:19:43,350 --> 00:19:48,450
if I do LS dash L it still prints the

491
00:19:46,890 --> 00:19:49,890
files in the current directory but it

492
00:19:48,450 --> 00:19:52,170
gives me a lot more information about

493
00:19:49,890 --> 00:19:54,600
those files and this is something you'll

494
00:19:52,170 --> 00:19:56,280
find yourself using quite a lot because

495
00:19:54,600 --> 00:20:00,810
the additional information it gives you

496
00:19:56,280 --> 00:20:02,010
is often quite handy let's look at what

497
00:20:00,810 --> 00:20:09,030
some of that information

498
00:20:02,010 --> 00:20:10,110
ah so first of all the D at the

499
00:20:09,030 --> 00:20:11,760
beginning of some of these entries

500
00:20:10,110 --> 00:20:14,820
indicate that something is a directory

501
00:20:11,760 --> 00:20:16,020
so the underscore data entry here for

502
00:20:14,820 --> 00:20:18,690
example is a directory

503
00:20:16,020 --> 00:20:22,650
whereas for for hTML is not a directory

504
00:20:18,690 --> 00:20:25,410
it's a file the following letters after

505
00:20:22,650 --> 00:20:28,650
that indicate the permissions that are

506
00:20:25,410 --> 00:20:30,810
set for that file so this like we saw

507
00:20:28,650 --> 00:20:32,640
earlier I might not be able to open a

508
00:20:30,810 --> 00:20:34,170
given file or I might not be able to CD

509
00:20:32,640 --> 00:20:35,760
into a given directory and this is all

510
00:20:34,170 --> 00:20:37,980
dictated by the permissions on that

511
00:20:35,760 --> 00:20:41,430
particular file or directory the way to

512
00:20:37,980 --> 00:20:43,500
read these is that the the first group

513
00:20:41,430 --> 00:20:45,810
of three are the permissions are set for

514
00:20:43,500 --> 00:20:49,560
the owner of the file all of these files

515
00:20:45,810 --> 00:20:52,020
you'll see are owned by me the second

516
00:20:49,560 --> 00:20:53,880
group of three characters is for the

517
00:20:52,020 --> 00:20:56,100
permissions for the group that owns this

518
00:20:53,880 --> 00:20:58,650
file in this case all of these files are

519
00:20:56,100 --> 00:21:01,770
also known by the john group and a final

520
00:20:58,650 --> 00:21:03,900
group of three is a list of the

521
00:21:01,770 --> 00:21:06,290
permissions for everyone else so anyone

522
00:21:03,900 --> 00:21:08,550
who's not a user owner or a group owner

523
00:21:06,290 --> 00:21:10,980
this directory is perhaps kind of boring

524
00:21:08,550 --> 00:21:14,190
because all of the things are owned by

525
00:21:10,980 --> 00:21:17,490
me but if we do something like CD to

526
00:21:14,190 --> 00:21:20,280
slash and do LS dash L you'll see that

527
00:21:17,490 --> 00:21:22,800
here all of them are owned by root we'll

528
00:21:20,280 --> 00:21:24,090
get back to what the root user is but

529
00:21:22,800 --> 00:21:26,400
here you see some of the permissions are

530
00:21:24,090 --> 00:21:31,410
a little bit more interesting the groups

531
00:21:26,400 --> 00:21:34,290
of three are read write and execute what

532
00:21:31,410 --> 00:21:36,450
these mean differs for files and for

533
00:21:34,290 --> 00:21:37,980
directories for files it's pretty

534
00:21:36,450 --> 00:21:40,170
straightforward if you have read

535
00:21:37,980 --> 00:21:41,820
permissions on a file then you can read

536
00:21:40,170 --> 00:21:43,950
its contents if you have write

537
00:21:41,820 --> 00:21:46,200
permissions on a file then you can save

538
00:21:43,950 --> 00:21:48,270
the file you can add more to it or you

539
00:21:46,200 --> 00:21:50,670
can replace it entirely and if you have

540
00:21:48,270 --> 00:21:52,620
execute to the X bit on a file then

541
00:21:50,670 --> 00:21:57,390
you're allowed to execute that file so

542
00:21:52,620 --> 00:22:00,030
if we do LS al in slash bin that's a

543
00:21:57,390 --> 00:22:02,640
novel and user bin you'll see that all

544
00:22:00,030 --> 00:22:04,590
of them have the execute bit set even

545
00:22:02,640 --> 00:22:06,480
for people who are not the owner of the

546
00:22:04,590 --> 00:22:08,280
file and this is because the echo

547
00:22:06,480 --> 00:22:09,420
program for example we want everyone on

548
00:22:08,280 --> 00:22:11,700
the computer to be able to execute

549
00:22:09,420 --> 00:22:13,920
there's no reason to say only certain

550
00:22:11,700 --> 00:22:15,570
users can run echo that doesn't really

551
00:22:13,920 --> 00:22:18,420
make any make any sense

552
00:22:15,570 --> 00:22:20,960
for directories though these permissions

553
00:22:18,420 --> 00:22:23,550
are a little bit different so read

554
00:22:20,960 --> 00:22:26,460
translates - are you allowed to see

555
00:22:23,550 --> 00:22:28,770
which files are inside this directory so

556
00:22:26,460 --> 00:22:30,530
think of read as lists for a directory

557
00:22:28,770 --> 00:22:33,420
are you allowed to list its contents

558
00:22:30,530 --> 00:22:36,210
write for a directory is whether you are

559
00:22:33,420 --> 00:22:39,090
allowed to rename create or remove files

560
00:22:36,210 --> 00:22:42,030
within that directory so it's still kind

561
00:22:39,090 --> 00:22:45,240
of right but notice that this means that

562
00:22:42,030 --> 00:22:47,580
if you have write permissions on a file

563
00:22:45,240 --> 00:22:49,950
but you do not have write permissions on

564
00:22:47,580 --> 00:22:52,080
its directory you cannot delete the file

565
00:22:49,950 --> 00:22:54,420
you can empty it but you cannot delete

566
00:22:52,080 --> 00:22:57,660
it because that would require writing to

567
00:22:54,420 --> 00:22:59,130
the directory itself and finally execute

568
00:22:57,660 --> 00:23:01,950
on directories is something that trips

569
00:22:59,130 --> 00:23:04,650
people up a lot execute on a directory

570
00:23:01,950 --> 00:23:07,230
is what's known as search and that's not

571
00:23:04,650 --> 00:23:10,200
terribly helpful a name but what that

572
00:23:07,230 --> 00:23:13,470
means is are you allowed to enter this

573
00:23:10,200 --> 00:23:15,240
directory if you want to get to a file

574
00:23:13,470 --> 00:23:16,670
if you want to open it or read it or

575
00:23:15,240 --> 00:23:20,310
write it whatever you want to do

576
00:23:16,670 --> 00:23:22,710
basically to CD into a directory you

577
00:23:20,310 --> 00:23:25,050
must have the execute permission on all

578
00:23:22,710 --> 00:23:28,170
parent directories of that directory and

579
00:23:25,050 --> 00:23:30,480
the directory itself so for example for

580
00:23:28,170 --> 00:23:34,080
me to access a file inside slash user

581
00:23:30,480 --> 00:23:35,820
slash bin such as user bin echo I must

582
00:23:34,080 --> 00:23:38,100
have executed on route I must have

583
00:23:35,820 --> 00:23:40,380
execute on user and I must have execute

584
00:23:38,100 --> 00:23:42,120
on bin if I do not have all those

585
00:23:40,380 --> 00:23:44,790
execute bits I will not be allowed to

586
00:23:42,120 --> 00:23:48,410
access that file because I won't be able

587
00:23:44,790 --> 00:23:50,670
to enter the directories along the way

588
00:23:48,410 --> 00:23:52,560
there are a number of other bits that

589
00:23:50,670 --> 00:23:55,320
you might come across like you might see

590
00:23:52,560 --> 00:23:58,020
esses or T's in these lists you might

591
00:23:55,320 --> 00:23:58,950
see LS those we can talk about in office

592
00:23:58,020 --> 00:24:01,260
hours if you're curious

593
00:23:58,950 --> 00:24:04,260
they will mostly not matter for anything

594
00:24:01,260 --> 00:24:05,670
you will do in this class but they are

595
00:24:04,260 --> 00:24:08,100
handy to know about so if you're curious

596
00:24:05,670 --> 00:24:11,340
about them look them up on your own or

597
00:24:08,100 --> 00:24:13,080
come ask us in office hours there are

598
00:24:11,340 --> 00:24:14,580
some other programs that are handy to

599
00:24:13,080 --> 00:24:16,200
know about oh sorry there's one more

600
00:24:14,580 --> 00:24:17,400
thing as I mentioned if you just have a

601
00:24:16,200 --> 00:24:19,470
dash it means you do not have that

602
00:24:17,400 --> 00:24:21,810
permission right so if it says for

603
00:24:19,470 --> 00:24:23,190
example our dash X it means that you

604
00:24:21,810 --> 00:24:27,390
have read and execute but you do not

605
00:24:23,190 --> 00:24:29,240
have right there are some other handy

606
00:24:27,390 --> 00:24:32,360
programs to know about at this point

607
00:24:29,240 --> 00:24:35,450
one of them is move or the MV command so

608
00:24:32,360 --> 00:24:39,350
if I CD back to missing semester here MV

609
00:24:35,450 --> 00:24:42,950
lets me rename a file and rename here

610
00:24:39,350 --> 00:24:45,320
takes two paths it takes the old path in

611
00:24:42,950 --> 00:24:47,870
the new path this is means that move

612
00:24:45,320 --> 00:24:49,970
lets you both rename a file like if you

613
00:24:47,870 --> 00:24:52,130
change the name of the file but not the

614
00:24:49,970 --> 00:24:54,290
directory or it lets you move a file to

615
00:24:52,130 --> 00:24:56,360
a completely different directory it just

616
00:24:54,290 --> 00:24:57,890
you give the path to the current file

617
00:24:56,360 --> 00:24:59,720
and the path to where you want that file

618
00:24:57,890 --> 00:25:02,720
to be and that can change its location

619
00:24:59,720 --> 00:25:05,480
and its name so for example I can move

620
00:25:02,720 --> 00:25:09,020
dot files dot MD to be food MD

621
00:25:05,480 --> 00:25:16,280
unhelpfully right and similarly I can

622
00:25:09,020 --> 00:25:19,370
move it back there's also the CP command

623
00:25:16,280 --> 00:25:21,860
the CP or copy is very similar it lets

624
00:25:19,370 --> 00:25:23,750
you copy a file CP also takes two

625
00:25:21,860 --> 00:25:25,610
arguments it takes the path you want to

626
00:25:23,750 --> 00:25:28,340
copy from and the path you want to copy

627
00:25:25,610 --> 00:25:30,890
to and these are full paths so I could

628
00:25:28,340 --> 00:25:32,960
use this for example to say I want to

629
00:25:30,890 --> 00:25:37,550
copy dot files out MD - dot dot slash

630
00:25:32,960 --> 00:25:39,710
food MD sure food MD and now if I do LS

631
00:25:37,550 --> 00:25:42,800
dot you'll see that there's a food MD

632
00:25:39,710 --> 00:25:44,600
file in that directory so CP as well

633
00:25:42,800 --> 00:25:47,780
take two paths it does not have to be in

634
00:25:44,600 --> 00:25:49,700
the same directory and similarly there's

635
00:25:47,780 --> 00:25:52,070
the RM command which lets you remove a

636
00:25:49,700 --> 00:25:54,050
file and there - you can give paths in

637
00:25:52,070 --> 00:25:56,750
this case I'm removing dot dot slash

638
00:25:54,050 --> 00:25:59,480
food you should be aware for removing

639
00:25:56,750 --> 00:26:01,940
especially on Linux removal is by

640
00:25:59,480 --> 00:26:05,000
default not recursive so you cannot

641
00:26:01,940 --> 00:26:07,100
remove a directory using RM you can pass

642
00:26:05,000 --> 00:26:09,320
the - our flag which lets you do a

643
00:26:07,100 --> 00:26:10,550
recursive remove and then give a path

644
00:26:09,320 --> 00:26:12,890
that you want to remove and it will

645
00:26:10,550 --> 00:26:16,370
remove everything below it there is also

646
00:26:12,890 --> 00:26:18,290
the RM dr dir command which lets you

647
00:26:16,370 --> 00:26:21,230
remove a directory but it only lets you

648
00:26:18,290 --> 00:26:22,970
remove that directory if it is empty so

649
00:26:21,230 --> 00:26:23,960
the idea here is to sort of be a safety

650
00:26:22,970 --> 00:26:25,429
mechanism for you so you don't

651
00:26:23,960 --> 00:26:28,610
accidentally throw away a bunch of your

652
00:26:25,429 --> 00:26:31,040
files and the final little command

653
00:26:28,610 --> 00:26:32,540
that's handy to use is make there which

654
00:26:31,040 --> 00:26:34,429
lets you create a new directory and as

655
00:26:32,540 --> 00:26:36,110
we talked about before you don't want to

656
00:26:34,429 --> 00:26:37,940
do something like this because it will

657
00:26:36,110 --> 00:26:40,580
create two directories for you one

658
00:26:37,940 --> 00:26:42,140
called my and one called photos if you

659
00:26:40,580 --> 00:26:42,980
actually want to create a directory like

660
00:26:42,140 --> 00:26:50,120
this you would either

661
00:26:42,980 --> 00:26:52,519
escape the space or quote the string if

662
00:26:50,120 --> 00:26:54,919
you ever want more information about how

663
00:26:52,519 --> 00:26:57,049
any command to basically on these

664
00:26:54,919 --> 00:26:58,220
platforms work there's a really handy

665
00:26:57,049 --> 00:27:00,649
command for that as well

666
00:26:58,220 --> 00:27:04,610
there is the program called man for

667
00:27:00,649 --> 00:27:06,409
manual pages this program takes as an

668
00:27:04,610 --> 00:27:09,080
argument the name of another program and

669
00:27:06,409 --> 00:27:12,019
gives you its manual page so for example

670
00:27:09,080 --> 00:27:14,990
we could do man LS and this shows us a

671
00:27:12,019 --> 00:27:16,730
manual page for LS you'll notice that in

672
00:27:14,990 --> 00:27:19,250
the case of LS it is fairly similar to

673
00:27:16,730 --> 00:27:20,870
what we got with LS - help but it's a

674
00:27:19,250 --> 00:27:23,570
little easier to navigate a little

675
00:27:20,870 --> 00:27:26,269
easier to read usually towards the

676
00:27:23,570 --> 00:27:28,639
bottom you will also get examples

677
00:27:26,269 --> 00:27:29,899
information about who wrote it where you

678
00:27:28,639 --> 00:27:32,389
can find more information and that sort

679
00:27:29,899 --> 00:27:32,990
of stuff one thing that can be confusing

680
00:27:32,389 --> 00:27:35,330
sometimes

681
00:27:32,990 --> 00:27:36,289
at least until a recent version where

682
00:27:35,330 --> 00:27:38,779
they added this three at the bottom

683
00:27:36,289 --> 00:27:41,389
which says Q to quit they do not use to

684
00:27:38,779 --> 00:27:43,279
say this you press Q to quit this

685
00:27:41,389 --> 00:27:48,169
program it can be really hard to quit it

686
00:27:43,279 --> 00:27:50,750
if you do not know that a handy keyboard

687
00:27:48,169 --> 00:27:52,970
shortcut here by the way is ctrl L which

688
00:27:50,750 --> 00:27:56,990
lets you clear your terminal and go back

689
00:27:52,970 --> 00:27:59,330
to the top so so far we've only talked

690
00:27:56,990 --> 00:28:01,370
about programs in isolation but where

691
00:27:59,330 --> 00:28:03,019
much of the power of the shell really

692
00:28:01,370 --> 00:28:06,380
comes through is once you start

693
00:28:03,019 --> 00:28:08,419
combining different programs right so

694
00:28:06,380 --> 00:28:10,789
rather than just like running CDE

695
00:28:08,419 --> 00:28:12,500
running LS and etc you might want to

696
00:28:10,789 --> 00:28:13,940
chain multiple programs together you

697
00:28:12,500 --> 00:28:15,980
might want to interact with files and

698
00:28:13,940 --> 00:28:19,309
have files operate in between programs

699
00:28:15,980 --> 00:28:21,200
and the way we can do this is using this

700
00:28:19,309 --> 00:28:24,620
notion of streams that the shell gives

701
00:28:21,200 --> 00:28:25,940
us every program by default has I'm

702
00:28:24,620 --> 00:28:28,610
gonna simplify a little and say two

703
00:28:25,940 --> 00:28:31,820
primary streams it has an input stream

704
00:28:28,610 --> 00:28:33,950
and an output stream by default the

705
00:28:31,820 --> 00:28:35,419
input stream is your keyboard basically

706
00:28:33,950 --> 00:28:36,860
the input stream is your terminal and

707
00:28:35,419 --> 00:28:38,929
whatever you type into your terminal is

708
00:28:36,860 --> 00:28:40,610
going to end up into the program and it

709
00:28:38,929 --> 00:28:42,049
has a default output stream which is

710
00:28:40,610 --> 00:28:44,330
whenever the program prints something

711
00:28:42,049 --> 00:28:46,279
it's gonna print to that stream and by

712
00:28:44,330 --> 00:28:48,470
default that is also your terminal this

713
00:28:46,279 --> 00:28:50,690
is why when I type echo hello it gets

714
00:28:48,470 --> 00:28:54,200
printed back to my terminal but the

715
00:28:50,690 --> 00:28:56,360
shell gives you a way to rewire these

716
00:28:54,200 --> 00:28:59,120
streams to change where the input

717
00:28:56,360 --> 00:29:00,980
output of a programmer pointed the way

718
00:28:59,120 --> 00:29:06,200
the most straightforward way you do this

719
00:29:00,980 --> 00:29:08,210
is using the angle bracket signs so you

720
00:29:06,200 --> 00:29:11,570
can write something like this or you can

721
00:29:08,210 --> 00:29:14,299
write something like this the left angle

722
00:29:11,570 --> 00:29:16,340
bracket indicates rewire the input for

723
00:29:14,299 --> 00:29:21,040
this program to be the contents of this

724
00:29:16,340 --> 00:29:23,600
file and the end angle bracket means

725
00:29:21,040 --> 00:29:27,559
rewire the output of the preceding

726
00:29:23,600 --> 00:29:28,580
program into this file so let's look at

727
00:29:27,559 --> 00:29:32,240
an example of what that would look like

728
00:29:28,580 --> 00:29:34,280
if I do echo hello I can say I want that

729
00:29:32,240 --> 00:29:36,710
context the content to be stored in a

730
00:29:34,280 --> 00:29:39,049
file called hello dot text and because I

731
00:29:36,710 --> 00:29:40,520
gave this is a relative path right this

732
00:29:39,049 --> 00:29:42,980
will construct a file in the current

733
00:29:40,520 --> 00:29:45,440
directory called hello text and at least

734
00:29:42,980 --> 00:29:47,780
in theory its contents should be the

735
00:29:45,440 --> 00:29:50,360
word hello so if I run this notice that

736
00:29:47,780 --> 00:29:52,100
nothing got printed to my output the

737
00:29:50,360 --> 00:29:52,700
previous time when I ran echo hello it

738
00:29:52,100 --> 00:29:55,340
printed hello

739
00:29:52,700 --> 00:29:57,799
now that hello is going gone into a file

740
00:29:55,340 --> 00:30:00,610
called hello text and I can verify this

741
00:29:57,799 --> 00:30:03,860
by using the program called cat so cat

742
00:30:00,610 --> 00:30:07,280
prints the contents of a file so I can

743
00:30:03,860 --> 00:30:11,059
do cat hello dot txt and there it shows

744
00:30:07,280 --> 00:30:13,220
me hello but cat is a is also something

745
00:30:11,059 --> 00:30:16,220
that supports this kind of wiring so I

746
00:30:13,220 --> 00:30:17,990
can say cat which by default just prints

747
00:30:16,220 --> 00:30:20,720
its input it just duplicates its input

748
00:30:17,990 --> 00:30:23,809
to its output I can say I want you to

749
00:30:20,720 --> 00:30:25,160
take your input from Hello text what

750
00:30:23,809 --> 00:30:26,990
will happen in this case is that the

751
00:30:25,160 --> 00:30:29,840
shell is going to open hello dot txt

752
00:30:26,990 --> 00:30:32,540
take its contents and set that to be the

753
00:30:29,840 --> 00:30:34,370
input of cat and then cat is going to

754
00:30:32,540 --> 00:30:36,500
just print that to its output which

755
00:30:34,370 --> 00:30:38,179
since I haven't rewired it is gonna be

756
00:30:36,500 --> 00:30:41,870
my terminal so this will just print

757
00:30:38,179 --> 00:30:43,549
hello to the output and I can use both

758
00:30:41,870 --> 00:30:45,470
of these at the same time so for example

759
00:30:43,549 --> 00:30:47,000
if I want to copy a file and I don't

760
00:30:45,470 --> 00:30:51,500
want to use the CP command for some

761
00:30:47,000 --> 00:30:54,470
reason I can do this and in this case

762
00:30:51,500 --> 00:30:56,540
I'm telling the cat program nothing at

763
00:30:54,470 --> 00:30:58,010
all I'm just saying do your normal thing

764
00:30:56,540 --> 00:30:59,960
right the cat program does not know

765
00:30:58,010 --> 00:31:02,150
anything about this redirection but I'm

766
00:30:59,960 --> 00:31:04,190
telling the shell to use hello dot txt as

767
00:31:02,150 --> 00:31:08,120
the input for cat and to write anything

768
00:31:04,190 --> 00:31:09,470
that cat prints - hello - dot txt again

769
00:31:08,120 --> 00:31:10,010
this prints nothing to my terminal

770
00:31:09,470 --> 00:31:13,340
but if

771
00:31:10,010 --> 00:31:15,620
cat hello to text I get the output as I

772
00:31:13,340 --> 00:31:20,630
would have expected which is a copy of

773
00:31:15,620 --> 00:31:23,390
the original file there is also a double

774
00:31:20,630 --> 00:31:26,570
end bracket which is append instead of

775
00:31:23,390 --> 00:31:27,380
just overwrite so you'll notice that I

776
00:31:26,570 --> 00:31:29,870
if I do

777
00:31:27,380 --> 00:31:32,300
cat hello dot txt - hello - dot txt

778
00:31:29,870 --> 00:31:34,160
again and then I cat hello2 dot txt it

779
00:31:32,300 --> 00:31:36,500
still just contains hello even though it

780
00:31:34,160 --> 00:31:38,750
already contained hello if I switch that

781
00:31:36,500 --> 00:31:41,090
to instead be a double end bracket it

782
00:31:38,750 --> 00:31:45,890
means append and if I now cat that file

783
00:31:41,090 --> 00:31:47,570
it has a hello twice these are pretty

784
00:31:45,890 --> 00:31:49,850
straightforward they're usually just

785
00:31:47,570 --> 00:31:51,590
ways to interact with files but where it

786
00:31:49,850 --> 00:31:53,420
gets really interesting is an additional

787
00:31:51,590 --> 00:31:56,150
operator the shell gives you called the

788
00:31:53,420 --> 00:32:00,020
pipe character so pipe is just a

789
00:31:56,150 --> 00:32:02,900
vertical bar and what pipe means is take

790
00:32:00,020 --> 00:32:05,300
the output of the program to the left

791
00:32:02,900 --> 00:32:09,650
and make it the input of the program to

792
00:32:05,300 --> 00:32:13,940
the right right so what does this look

793
00:32:09,650 --> 00:32:17,450
like well let's take the example of ls /

794
00:32:13,940 --> 00:32:19,550
or ls dash l / this prints a bunch of

795
00:32:17,450 --> 00:32:22,460
things let's say that I only wanted the

796
00:32:19,550 --> 00:32:25,670
last line of this output well there's a

797
00:32:22,460 --> 00:32:28,940
command called tail and tail prints the

798
00:32:25,670 --> 00:32:32,420
last n lines of its input and I can do

799
00:32:28,940 --> 00:32:34,520
-n1 so this is a flag called n you

800
00:32:32,420 --> 00:32:36,890
can also use dash dash lines if you want

801
00:32:34,520 --> 00:32:38,660
to use it as a longer option but in this

802
00:32:36,890 --> 00:32:42,260
case this is saying just print the last

803
00:32:38,660 --> 00:32:46,640
line and I can wire these together so I

804
00:32:42,260 --> 00:32:50,840
can say ls dash l / pipe tail -n1

805
00:32:46,640 --> 00:32:53,060
and notice here that ls does not know

806
00:32:50,840 --> 00:32:55,340
about tail and tail does not know about

807
00:32:53,060 --> 00:32:56,870
ls they are different programs and have

808
00:32:55,340 --> 00:32:59,120
never been programmed to be compatible

809
00:32:56,870 --> 00:33:00,650
with one another all they know how to do

810
00:32:59,120 --> 00:33:02,900
is read from input and write to output

811
00:33:00,650 --> 00:33:05,360
and then the pipe is what wires them

812
00:33:02,900 --> 00:33:07,670
together and in this particular case I'm

813
00:33:05,360 --> 00:33:09,380
saying I want the output of LS to be the

814
00:33:07,670 --> 00:33:10,850
input to tail and then I want the output

815
00:33:09,380 --> 00:33:12,140
of tail to just go to my terminal

816
00:33:10,850 --> 00:33:14,240
because I haven't rewired it

817
00:33:12,140 --> 00:33:16,730
I could also rewire this to say I want

818
00:33:14,240 --> 00:33:18,770
the output to go to ls dot text and in this

819
00:33:16,730 --> 00:33:20,990
case if I cat ls dot text I would get

820
00:33:18,770 --> 00:33:22,640
the appropriate output and it turns out

821
00:33:20,990 --> 00:33:21,815
you can do some really neat things with this

822
00:33:23,340 --> 00:33:27,720
gonna cover this a lot more in the data

823
00:33:25,110 --> 00:33:30,720
wrangling lecture there will be in like

824
00:33:27,720 --> 00:33:32,490
four days or something on the kind of

825
00:33:30,720 --> 00:33:36,060
fancy stuff you can do when you start

826
00:33:32,490 --> 00:33:37,560
building more advanced pipelines one to

827
00:33:36,060 --> 00:33:42,300
give you one example we can do something

828
00:33:37,560 --> 00:33:46,320
like curl - -head --silent google.com

829
00:33:42,300 --> 00:33:48,870
so just to show you what that looks

830
00:33:46,320 --> 00:33:52,680
like this gives me all the HTTP headers

831
00:33:48,870 --> 00:33:56,520
for accessing google.com and I can pipe

832
00:33:52,680 --> 00:34:01,260
that to grep a - like a --ignore-case

833
00:33:56,520 --> 00:34:04,230
or just -i if I want content

834
00:34:01,260 --> 00:34:06,120
length so this is gonna print the

835
00:34:04,230 --> 00:34:07,500
content length header, grep is a program

836
00:34:06,120 --> 00:34:09,090
that we'll talk about later they'll let

837
00:34:07,500 --> 00:34:12,660
you search in an input stream for a

838
00:34:09,090 --> 00:34:15,560
given keyword we can pipe that through

839
00:34:12,660 --> 00:34:20,190
say the cut command which takes a

840
00:34:15,560 --> 00:34:22,260
delimiter set that to be space and I

841
00:34:20,190 --> 00:34:24,420
want the second field and this prints

842
00:34:22,260 --> 00:34:25,950
just the content length this is sort of

843
00:34:24,420 --> 00:34:28,380
a silly example right like this just

844
00:34:25,950 --> 00:34:30,180
lets you extract the content length in

845
00:34:28,380 --> 00:34:32,700
bytes of google.com from the command

846
00:34:30,180 --> 00:34:34,740
line it's not a very useful thing to do

847
00:34:32,700 --> 00:34:36,300
but you can see how by chaining these

848
00:34:34,740 --> 00:34:38,330
together you can achieve a bunch of

849
00:34:36,300 --> 00:34:40,980
really interesting text manipulation

850
00:34:38,330 --> 00:34:43,290
effects and it turns out pipes are not

851
00:34:40,980 --> 00:34:45,330
just for textual data you can do this

852
00:34:43,290 --> 00:34:47,850
for things like images as well you can

853
00:34:45,330 --> 00:34:49,590
have a program that manipulates a binary

854
00:34:47,850 --> 00:34:51,450
image on its input and writes a binary

855
00:34:49,590 --> 00:34:53,400
image to its output and you can chain

856
00:34:51,450 --> 00:34:54,840
them together in this way and we'll talk

857
00:34:53,400 --> 00:34:57,000
about some of those kinds of examples

858
00:34:54,840 --> 00:34:59,430
later on - you can even do this for

859
00:34:57,000 --> 00:35:00,900
video if you want you can stream this is

860
00:34:59,430 --> 00:35:02,940
for example a great way if you have a

861
00:35:00,900 --> 00:35:05,790
chromecast at home you can stream a

862
00:35:02,940 --> 00:35:07,920
video file like this by having the last

863
00:35:05,790 --> 00:35:11,160
program in your pipe be a chromecast

864
00:35:07,920 --> 00:35:13,050
send program so you stream a video file

865
00:35:11,160 --> 00:35:19,140
into it and it streams or HTTP to your

866
00:35:13,050 --> 00:35:20,370
chromecast we'll take we'll talk a lot

867
00:35:19,140 --> 00:35:22,410
more about this in the data wrangling

868
00:35:20,370 --> 00:35:25,110
lecture but there's one more thing that

869
00:35:22,410 --> 00:35:27,800
I wanted to talk to you about about sort

870
00:35:25,110 --> 00:35:30,390
of how to use the terminal and a more

871
00:35:27,800 --> 00:35:31,920
interesting and perhaps more powerful

872
00:35:30,390 --> 00:35:33,840
way that you might be used to and this

873
00:35:31,920 --> 00:35:35,640
is perhaps even going to be interesting

874
00:35:33,840 --> 00:35:37,720
for the ones of you who feel like you're

875
00:35:35,640 --> 00:35:41,020
already comfortable with the term

876
00:35:37,720 --> 00:35:43,030
but first we need to cover a important

877
00:35:41,020 --> 00:35:44,890
topic when it comes to Linux systems and

878
00:35:43,030 --> 00:35:47,620
Mac OS systems in particular which is

879
00:35:44,890 --> 00:35:49,300
the notion of the root user the root

880
00:35:47,620 --> 00:35:52,480
user is sort of like the administrator

881
00:35:49,300 --> 00:35:55,000
user on Windows and it has user IDs zero

882
00:35:52,480 --> 00:35:56,830
the root user is special because it is

883
00:35:55,000 --> 00:35:59,680
allowed to do whatever it wants on your

884
00:35:56,830 --> 00:36:01,540
system even if a file is like not

885
00:35:59,680 --> 00:36:03,790
readable by anyone or if it's not

886
00:36:01,540 --> 00:36:06,010
writable by anyone root can still access

887
00:36:03,790 --> 00:36:09,000
that file root is sort of a super user

888
00:36:06,010 --> 00:36:11,260
that gets to do whatever they want and

889
00:36:09,000 --> 00:36:13,330
most of the time you will not be

890
00:36:11,260 --> 00:36:15,550
operating as the super user you will not

891
00:36:13,330 --> 00:36:17,350
be root you will be a user like John or

892
00:36:15,550 --> 00:36:19,660
whatever your name is and that's going

893
00:36:17,350 --> 00:36:21,370
to be the user you act with because if

894
00:36:19,660 --> 00:36:23,470
you were operating your computer as the

895
00:36:21,370 --> 00:36:24,700
root user at all times if you ran the

896
00:36:23,470 --> 00:36:26,710
wrong program they could just completely

897
00:36:24,700 --> 00:36:29,950
destroy your computer and you don't want

898
00:36:26,710 --> 00:36:31,810
that right but every now and again you

899
00:36:29,950 --> 00:36:34,450
want to do something that requires that

900
00:36:31,810 --> 00:36:38,580
you are root usually for these cases you

901
00:36:34,450 --> 00:36:42,790
will use a program called sudo su do or

902
00:36:38,580 --> 00:36:44,740
do as su and su in this case is Super

903
00:36:42,790 --> 00:36:46,590
User so this is a way to do the

904
00:36:44,740 --> 00:36:49,750
following thing as the super user

905
00:36:46,590 --> 00:36:51,490
usually the way sudo works is you write

906
00:36:49,750 --> 00:36:53,020
sudo and then a command like you would

907
00:36:51,490 --> 00:36:54,580
normally on your terminal and it will

908
00:36:53,020 --> 00:36:56,230
just run that command as if you were

909
00:36:54,580 --> 00:37:01,180
root as opposed to the user you actually

910
00:36:56,230 --> 00:37:04,540
are where might you need something like

911
00:37:01,180 --> 00:37:05,800
this well there is a special there are

912
00:37:04,540 --> 00:37:07,510
many special file system on your

913
00:37:05,800 --> 00:37:11,070
computer but in particular there's one

914
00:37:07,510 --> 00:37:14,800
called sysfs if you CD to slash sys

915
00:37:11,070 --> 00:37:17,320
this is a whole new world this file

916
00:37:14,800 --> 00:37:19,720
system is are not actually files on your

917
00:37:17,320 --> 00:37:22,120
computer instead these are various

918
00:37:19,720 --> 00:37:24,180
kernel parameters so the kernel is like

919
00:37:22,120 --> 00:37:26,680
basically the the core of your computer

920
00:37:24,180 --> 00:37:29,560
this is a way for you to access various

921
00:37:26,680 --> 00:37:32,680
kernel parameters through what looks

922
00:37:29,560 --> 00:37:35,950
like a file system you'll see here that

923
00:37:32,680 --> 00:37:37,690
if I CD into class for example it has

924
00:37:35,950 --> 00:37:39,880
directories for a bunch of different

925
00:37:37,690 --> 00:37:43,750
types of devices that I can interact

926
00:37:39,880 --> 00:37:47,920
with or various queues I can access or all

927
00:37:43,750 --> 00:37:49,990
sorts of weird knobs internally and

928
00:37:47,920 --> 00:37:50,410
because they're exposed as files it means

929
00:37:50,410 --> 00:37:54,280
we can also use all the tools have been

930
00:37:52,030 --> 00:37:57,579
using so far in order to manipulate them

931
00:37:54,280 --> 00:38:01,420
one example of this is if you go into

932
00:37:57,579 --> 00:38:02,440
sys class backlight so this backlight

933
00:38:01,420 --> 00:38:04,180
directly and lets you configure the

934
00:38:02,440 --> 00:38:06,760
backlight on your laptop if you have one

935
00:38:04,180 --> 00:38:08,920
so I can CD in to intel backlight this

936
00:38:06,760 --> 00:38:10,990
is an Intel laptop inside here you'll

937
00:38:08,920 --> 00:38:12,760
see there's a file called brightness and

938
00:38:10,990 --> 00:38:16,089
I can cat the brightness this is the

939
00:38:12,760 --> 00:38:18,880
current brightness of my screen but not

940
00:38:16,089 --> 00:38:21,460
only that I can modify this too in order

941
00:38:18,880 --> 00:38:23,740
to change the brightness of my screen so

942
00:38:21,460 --> 00:38:25,750
you might think that I could do let's

943
00:38:23,740 --> 00:38:26,799
see what the max brightness is here okay

944
00:38:25,750 --> 00:38:29,589
so it's currently set to the max

945
00:38:26,799 --> 00:38:32,319
brightness you might imagine that I

946
00:38:29,589 --> 00:38:35,410
could do something like if I do echo

947
00:38:32,319 --> 00:38:39,010
let's do half or something

948
00:38:35,410 --> 00:38:38,010
echo 500 to brightness

949
00:38:38,010 --> 00:38:39,010
if I do this it says

950
00:38:39,010 --> 00:38:43,089
permission denied I'm not allowed to

951
00:38:40,839 --> 00:38:45,220
modify brightness because in order to

952
00:38:43,089 --> 00:38:46,599
basically in order to change things in

953
00:38:45,220 --> 00:38:48,460
the kernel you need to be the

954
00:38:46,599 --> 00:38:50,619
administrator and you might imagine that

955
00:38:48,460 --> 00:38:52,960
the way to solve this is to write sudo

956
00:38:50,619 --> 00:38:55,779
echo 500 but I still get a permission

957
00:38:52,960 --> 00:38:58,260
denied error but why is that it's

958
00:38:55,779 --> 00:39:00,549
because as I mentioned before these

959
00:38:58,260 --> 00:39:03,069
redirections of input and output is not

960
00:39:00,549 --> 00:39:05,470
something the programs know about when

961
00:39:03,069 --> 00:39:07,240
we piped Elison to tail tail did not

962
00:39:05,470 --> 00:39:09,609
know about LS and LS did not know about

963
00:39:07,240 --> 00:39:11,859
tail the pipe and the redirection was

964
00:39:09,609 --> 00:39:14,079
set up by the shell so in this case

965
00:39:11,859 --> 00:39:18,039
what's happening is I'm telling my shell

966
00:39:14,079 --> 00:39:21,220
run the program sudo with the arguments

967
00:39:18,039 --> 00:39:24,130
echo and 500 and send its output to the

968
00:39:21,220 --> 00:39:25,930
file called brightness but the shell is

969
00:39:24,130 --> 00:39:29,410
what is opening the brightness file it

970
00:39:25,930 --> 00:39:32,380
is not the sudo program so in this case

971
00:39:29,410 --> 00:39:33,789
the shell which is running as me tries

972
00:39:32,380 --> 00:39:35,470
to open the brightness file for writing

973
00:39:33,789 --> 00:39:37,079
and it's not allowed to do that and

974
00:39:35,470 --> 00:39:39,779
therefore I get a permission down error

975
00:39:37,079 --> 00:39:42,339
you might have seen this if you like

976
00:39:39,779 --> 00:39:43,750
search for something end up on Stack

977
00:39:42,339 --> 00:39:45,400
Overflow and it tells just run this

978
00:39:43,750 --> 00:39:47,440
command and you'll see that it does

979
00:39:45,400 --> 00:39:52,930
something like they give you

980
00:39:47,440 --> 00:39:57,970
instructions like one two sis what's an

981
00:39:52,930 --> 00:39:59,559
example net ipv4 for word for example

982
00:39:57,970 --> 00:40:02,589
this is something you may have seen if

983
00:39:59,559 --> 00:40:04,240
you're setting up a firewall and this

984
00:40:02,589 --> 00:40:05,680
command is intended to work

985
00:40:04,240 --> 00:40:08,200
because this little pound symbol

986
00:40:05,680 --> 00:40:09,640
indicates run this as root this is

987
00:40:08,200 --> 00:40:11,170
something that is very rarely explained

988
00:40:09,640 --> 00:40:12,970
but that is what the pound symbol means

989
00:40:11,170 --> 00:40:15,099
you'll see on my prompt there's a dollar

990
00:40:12,970 --> 00:40:17,710
symbol instead and the dollar indicates

991
00:40:15,099 --> 00:40:18,819
you are not running as root so the

992
00:40:17,710 --> 00:40:22,270
question is how do I get around this

993
00:40:18,819 --> 00:40:24,690
well I could switch into a root terminal

994
00:40:22,270 --> 00:40:27,369
so one way to do this is to run sudo su

995
00:40:24,690 --> 00:40:32,140
sudo su is saying run the following

996
00:40:27,369 --> 00:40:34,329
command s root and su is a complicated

997
00:40:32,140 --> 00:40:37,290
command that effectively gets you a

998
00:40:34,329 --> 00:40:40,599
shell as the super user so if I do this

999
00:40:37,290 --> 00:40:42,010
type of password then now you'll see

1000
00:40:40,599 --> 00:40:44,530
that the username at the beginning

1001
00:40:42,010 --> 00:40:47,109
changed from jon to root and the prompt

1002
00:40:44,530 --> 00:40:49,390
changed from a dollar to a pound if I

1003
00:40:47,109 --> 00:40:52,240
now I come in to that file if I do echo

1004
00:40:49,390 --> 00:40:54,010
500 to brightness my screen got a little

1005
00:40:52,240 --> 00:40:57,040
dimmer but you can't see it you just

1006
00:40:54,010 --> 00:40:58,990
have to trust me and now I didn't get an

1007
00:40:57,040 --> 00:41:01,630
error and this is because the shell is

1008
00:40:58,990 --> 00:41:04,540
now running as root it is not running as

1009
00:41:01,630 --> 00:41:07,359
Jon and the root user is allowed to open

1010
00:41:04,540 --> 00:41:09,760
this file but given our knowledge that

1011
00:41:07,359 --> 00:41:11,349
we have of the terminal now there's

1012
00:41:09,760 --> 00:41:13,720
actually a way for us to do this without

1013
00:41:11,349 --> 00:41:19,119
having to drop to a root shell and that

1014
00:41:13,720 --> 00:41:22,990
is as follows that's I guess restore it

1015
00:41:19,119 --> 00:41:26,589
to 1060 so do you see why this is

1016
00:41:22,990 --> 00:41:29,020
different here I'm telling my shell to

1017
00:41:26,589 --> 00:41:31,270
run the echo 1060 command which is gonna

1018
00:41:29,020 --> 00:41:33,369
echo 1060 and I'm telling it to run the

1019
00:41:31,270 --> 00:41:35,890
sudo tee brightness command and I'm

1020
00:41:33,369 --> 00:41:39,160
telling you to send the output of echo

1021
00:41:35,890 --> 00:41:40,540
into sudo tee in order to understand this

1022
00:41:39,160 --> 00:41:43,450
you need to know what the tee command does

1023
00:41:40,540 --> 00:41:47,079
the tee command takes its input and writes

1024
00:41:43,450 --> 00:41:49,540
it to a file but also to standard out so

1025
00:41:47,079 --> 00:41:52,329
tee is a convenient way if you have say a

1026
00:41:49,540 --> 00:41:54,160
log file that you want to like send to a

1027
00:41:52,329 --> 00:41:56,230
file to store for later but you also

1028
00:41:54,160 --> 00:41:58,059
want to see it to yourself then you can

1029
00:41:56,230 --> 00:41:59,770
pipe it through tee give it the name of a

1030
00:41:58,059 --> 00:42:01,809
file and it will write whatever its

1031
00:41:59,770 --> 00:42:04,270
input is both to that file and to your

1032
00:42:01,809 --> 00:42:07,630
screen and here I'm taking advantage of

1033
00:42:04,270 --> 00:42:09,940
that program I'm saying run tee as route

1034
00:42:07,630 --> 00:42:12,970
and have tee right into the brightness

1035
00:42:09,940 --> 00:42:14,380
file and so in this case the tee program

1036
00:42:12,970 --> 00:42:16,150
which is what is opening the brightness

1037
00:42:14,380 --> 00:42:17,370
file is running as root and so it is

1038
00:42:16,150 --> 00:42:20,190
allowed to do

1039
00:42:17,370 --> 00:42:21,390
if I run this it will now again you

1040
00:42:20,190 --> 00:42:23,850
can't see but the brightness and I've

1041
00:42:21,390 --> 00:42:25,770
been turned on by a laptop and I don't

1042
00:42:23,850 --> 00:42:27,390
get any errors and I never had to drop

1043
00:42:25,770 --> 00:42:30,930
into a root shell and run commands there

1044
00:42:27,390 --> 00:42:32,160
which can often be somewhat dangerous if

1045
00:42:30,930 --> 00:42:33,450
you want to explore this filesystem a

1046
00:42:32,160 --> 00:42:35,940
little bit more there's a lot of

1047
00:42:33,450 --> 00:42:39,450
interesting stuff in here if you just

1048
00:42:35,940 --> 00:42:41,430
sort of start browsing around you can

1049
00:42:39,450 --> 00:42:42,930
find all sorts of fun things so for

1050
00:42:41,430 --> 00:42:45,090
example we noticed that there was a fun

1051
00:42:42,930 --> 00:42:48,540
brightness command here I wonder what

1052
00:42:45,090 --> 00:42:49,980
other kinds of brightness I can set so I

1053
00:42:48,540 --> 00:42:51,860
can use the find command which we will

1054
00:42:49,980 --> 00:42:56,000
also talk about in a coming lecture I

1055
00:42:51,860 --> 00:42:58,860
wouldn't look on any file whose name

1056
00:42:56,000 --> 00:43:01,890
it's a little like brightness in the

1057
00:42:58,860 --> 00:43:05,070
current directory that's unhelpful maybe

1058
00:43:01,890 --> 00:43:08,850
they're not files did I misspell

1059
00:43:05,070 --> 00:43:17,010
brightness yeah why is it being annoying

1060
00:43:08,850 --> 00:43:20,460
Oh apparently it does not want to search

1061
00:43:17,010 --> 00:43:23,910
for brightness for me how well luckily

1062
00:43:20,460 --> 00:43:27,480
for you I know of one already handy that

1063
00:43:23,910 --> 00:43:30,090
there is a subdirectory called LEDs and

1064
00:43:27,480 --> 00:43:32,400
LEDs have brightness too what kind of

1065
00:43:30,090 --> 00:43:36,960
LEDs are there ooh lots of things for

1066
00:43:32,400 --> 00:43:38,280
example the scroll lock led now most of

1067
00:43:36,960 --> 00:43:40,290
you probably don't know what the scroll

1068
00:43:38,280 --> 00:43:42,780
lock LED is or much less what scroll

1069
00:43:40,290 --> 00:43:45,770
lock is you might have seen a key on

1070
00:43:42,780 --> 00:43:47,670
your keyboard neighbor named scroll lock

1071
00:43:45,770 --> 00:43:49,650
basically no one knows what it means

1072
00:43:47,670 --> 00:43:51,750
anymore no one really uses it for

1073
00:43:49,650 --> 00:43:55,680
anything it's mostly just a dead key and

1074
00:43:51,750 --> 00:43:57,240
also a dead LED what if you wanted to

1075
00:43:55,680 --> 00:43:59,220
configure it so that every time you get

1076
00:43:57,240 --> 00:44:00,960
email your scroll lock LED lights up

1077
00:43:59,220 --> 00:44:03,270
because there's no other reason why it

1078
00:44:00,960 --> 00:44:06,000
would light up well if we seed you into

1079
00:44:03,270 --> 00:44:08,130
this particular directory that has a

1080
00:44:06,000 --> 00:44:12,320
brightness place and it's set to zero

1081
00:44:08,130 --> 00:44:12,320
well what happens if I write one into it

1082
00:44:12,590 --> 00:44:17,220
you probably should not just be writing

1083
00:44:15,330 --> 00:44:18,720
random numbers into random files in this

1084
00:44:17,220 --> 00:44:20,310
directory because you are affecting your

1085
00:44:18,720 --> 00:44:22,560
kernel directly like look up what the

1086
00:44:20,310 --> 00:44:24,240
files do in this particular case I have

1087
00:44:22,560 --> 00:44:28,050
warned safety goggles and I've done my

1088
00:44:24,240 --> 00:44:30,630
research so now you can't tell but on my

1089
00:44:28,050 --> 00:44:33,509
keyboard the scroll lock LED is now lit

1090
00:44:30,630 --> 00:44:35,400
so now if I wrote a program that like

1091
00:44:33,509 --> 00:44:37,829
did some checking of mail and stuff I

1092
00:44:35,400 --> 00:44:40,229
could have it at the end run a program

1093
00:44:37,829 --> 00:44:43,499
that echoes one into this file and now I

1094
00:44:40,229 --> 00:44:47,460
have a way for my led to my keyboard to

1095
00:44:43,499 --> 00:44:49,680
indicate when I've new email at this

1096
00:44:47,460 --> 00:44:50,940
point you should know roughly your way

1097
00:44:49,680 --> 00:44:54,269
around

1098
00:44:50,940 --> 00:44:56,249
the terminal around the shell and and

1099
00:44:54,269 --> 00:44:58,920
know enough to accomplish these basic

1100
00:44:56,249 --> 00:45:01,289
tasks at least in theory now you

1101
00:44:58,920 --> 00:45:02,819
shouldn't need to use like

1102
00:45:01,289 --> 00:45:03,420
point-and-click interfaces to find files

1103
00:45:02,819 --> 00:45:05,279
anymore

1104
00:45:03,420 --> 00:45:07,470
there's one remaining trick you might

1105
00:45:05,279 --> 00:45:10,529
need and that is the ability to open a

1106
00:45:07,470 --> 00:45:13,950
file so far I've only really given you

1107
00:45:10,529 --> 00:45:17,690
ways to find files but one thing you

1108
00:45:13,950 --> 00:45:21,420
should know about is missing semester

1109
00:45:17,690 --> 00:45:23,640
xdg-open this will probably only work

1110
00:45:21,420 --> 00:45:27,119
on Linux on Mac OS I think it's just

1111
00:45:23,640 --> 00:45:29,430
called open on Windows who knows

1112
00:45:27,119 --> 00:45:31,739
xdg-open you give the name of a file and

1113
00:45:29,430 --> 00:45:34,769
it will open it in the appropriate program

1114
00:45:31,739 --> 00:45:36,180
so if you open if you do xdg-open an

1115
00:45:34,769 --> 00:45:39,269
HTML file that will open your browser

1116
00:45:36,180 --> 00:45:41,039
and open that file and once you have

1117
00:45:39,269 --> 00:45:42,869
that program in theory you should no

1118
00:45:41,039 --> 00:45:45,059
longer need to open like a Finder window

1119
00:45:42,869 --> 00:45:46,799
ever again you might want to for other

1120
00:45:45,059 --> 00:45:48,180
reasons but in theory you can accomplish

1121
00:45:46,799 --> 00:45:50,789
at all using the tools that we've

1122
00:45:48,180 --> 00:45:53,849
learned today this might all seem

1123
00:45:50,789 --> 00:45:55,589
relatively basic for some of you but as

1124
00:45:53,849 --> 00:45:57,479
I mentioned this is sort of the ramp-up

1125
00:45:55,589 --> 00:45:59,460
period of now we all know how the shell

1126
00:45:57,479 --> 00:46:01,979
works and a lot of what we'll be doing

1127
00:45:59,460 --> 00:46:03,450
in future lectures is using this

1128
00:46:01,979 --> 00:46:07,019
knowledge to do really interesting

1129
00:46:03,450 --> 00:46:09,450
things using the shell that sort of this

1130
00:46:07,019 --> 00:46:10,979
is learning the the interface that we're

1131
00:46:09,450 --> 00:46:14,849
going to be using and so it's important

1132
00:46:10,979 --> 00:46:16,650
we all know it we're gonna talk a lot

1133
00:46:14,849 --> 00:46:18,269
more in the next lecture about how to

1134
00:46:16,650 --> 00:46:20,309
automate tasks like this how to write

1135
00:46:18,269 --> 00:46:22,140
scripts that run a bunch of programs for

1136
00:46:20,309 --> 00:46:24,390
you and have to do things like

1137
00:46:22,140 --> 00:46:26,700
conditionals and loops and stuff in your

1138
00:46:24,390 --> 00:46:29,009
terminal and do things like run a

1139
00:46:26,700 --> 00:46:30,390
program until it fails which can be

1140
00:46:29,009 --> 00:46:31,979
handy in classes where you want to run

1141
00:46:30,390 --> 00:46:35,369
something until your test suite fails

1142
00:46:31,979 --> 00:46:38,550
for example so that's the topic for next

1143
00:46:35,369 --> 00:46:39,900
week's lecture did you have a question

1144
00:46:38,550 --> 00:46:42,420
it's what you've been demoing this

1145
00:46:39,900 --> 00:46:49,770
assist directory that presumably will

1146
00:46:42,420 --> 00:46:52,530
only work if you're running that is a

1147
00:46:49,770 --> 00:46:55,440
good question I don't know whether the

1148
00:46:52,530 --> 00:46:57,570
windows subsystem for Linux will expose

1149
00:46:55,440 --> 00:46:59,280
the sis file system if it does it

1150
00:46:57,570 --> 00:47:03,180
probably only exposes a very small

1151
00:46:59,280 --> 00:47:08,490
number of things it might because there

1152
00:47:03,180 --> 00:47:10,320
are I don't know check it out

1153
00:47:08,490 --> 00:47:11,610
one thing you'll see is the lecture

1154
00:47:10,320 --> 00:47:14,370
notes for this lecture are already

1155
00:47:11,610 --> 00:47:16,770
online and at the very bottom of the

1156
00:47:14,370 --> 00:47:18,420
file there are a bunch of exercises some

1157
00:47:16,770 --> 00:47:20,190
of them are relatively easy some of them

1158
00:47:18,420 --> 00:47:22,560
are a little bit harder and what we

1159
00:47:20,190 --> 00:47:24,060
encourage you to do is to take a stab at

1160
00:47:22,560 --> 00:47:25,410
going through them if you know this

1161
00:47:24,060 --> 00:47:27,660
stuff already it should go really

1162
00:47:25,410 --> 00:47:29,400
quickly if you don't it might teach you

1163
00:47:27,660 --> 00:47:31,740
a bunch of things that you might not

1164
00:47:29,400 --> 00:47:33,150
realize you didn't know and for the

1165
00:47:31,740 --> 00:47:35,190
office hours that we're gonna do right

1166
00:47:33,150 --> 00:47:36,840
after this lecture we will happily help

1167
00:47:35,190 --> 00:47:38,160
you get through all of those or if there

1168
00:47:36,840 --> 00:47:39,540
are other commands and you learn in the

1169
00:47:38,160 --> 00:47:42,300
process you want to know how to use more

1170
00:47:39,540 --> 00:47:44,910
efficiently and then in next lecture

1171
00:47:42,300 --> 00:47:46,710
which is tomorrow will basically be

1172
00:47:44,910 --> 00:47:48,290
assuming that you know the kind of stuff

1173
00:47:46,710 --> 00:47:51,750
that the exercise is going to teach you

1174
00:47:48,290 --> 00:47:53,030
there's also a an email address on the

1175
00:47:51,750 --> 00:47:56,100
website where you can send us questions

1176
00:47:53,030 --> 00:47:58,860
if you think of something like after the

1177
00:47:56,100 --> 00:48:05,160
office hours are finished are there any

1178
00:47:58,860 --> 00:48:07,050
questions before we end today no no all

1179
00:48:05,160 --> 00:48:09,480
right well we will have office hours on

1180
00:48:07,050 --> 00:48:12,150
the ninth floor of the gates building of

1181
00:48:09,480 --> 00:48:15,830
building 32 in like five minutes

1182
00:48:12,150 --> 00:48:15,830
sweet see you there